spmi: pm: drop bus-level PM suspend/resume routines

SPMI defines the behavior of a device in the "SLEEP" state as being
"user-defined or specified by the device manufacturer".  Without
clearly-defined bus-level semantics for low-power states, push the
responsibility of transitioning a device into/out of "SLEEP" into SPMI
device drivers.

Cc: Felipe Balbi <balbi@ti.com>
Signed-off-by: Josh Cartwright <joshc@codeaurora.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>